This disclosure relates to aircraft in general, and in particular, to morphing aircraft having a deployable lifting surface, such as a wing, that is laterally extendable and retractable relative to a main aircraft lifting body, and which, when retracted, fairs smoothly into the outer mold line surface of the main body and thereby imparts low-aspect-ratio, high-speed aerodynamic characteristics to the aircraft, and when extended, imparts high-aspect-ratio, low-speed aerodynamic characteristics to the aircraft.
It has long been recognized that fixed wing aircraft have limitations as regards to their operational capabilities, performance, mission flexibility, and mission durations. Accordingly, efforts have been made to develop more versatile products to better meet existing and even more demanding future manned and unmanned mission requirements of, e.g., unmanned combat air vehicles (UCAV). One such effort is the development of so-called “morphing aircraft,” i.e., air-craft with the ability to adapt and optimize their shape to achieve dissimilar, multi-objective mission roles efficiently and effectively.
Over the years, several morphing aircraft concepts have been developed and used to accommodate both low and high speed mission requirements. One type of production aircraft configuration found in, e.g., the Grumman F-14 “Tomcat” and the General Dynamics F-111B “Aardvark,” involves a variable sweep wing, movable between a forward sweep position for low speed operations and an aft sweep position for high speed operation.
However, prior solutions that use a swept wing change the location of the center of lift (CL) with respect to the vehicles' longitudinal axis, and hence, its center of gravity (CG). The sweeping action moves the resultant lift of the aircraft along the aircraft's longitudinal axis, thereby adversely impacting the aerodynamic stability of the aircraft, which then must be compensated for by activating flight control surfaces, resulting in an increase in drag or by moving weight (such as fuel) from one location to another. Also, since the wing remains external to the vehicle's fuselage, the wing always provides some lifting surface regardless of its position. Thus, the wetted area of a variable swept-wing aircraft remains approximately the same in the swept and un-swept configurations, thereby generating relatively high drag even during high speed operations.
Another morphing aircraft configuration uses a partially vertically folded wing to reduce lift-generating wing area during high speed operations. However, since all wing surfaces are still exposed to airflow and the wetted area of the wing remains approximately the same for both low and high speed configurations, unnecessary and wasteful drag is generated at high speeds.
Still another aircraft configuration currently under development employs a variable wing shape configuration, using multiple actuators and flexible wing skins to change the sweep and chord depth of the wing. However, this arrangement requires extensive kinematics, greatly increasing the complexity, weight and associated costs to manufacture, maintain and operate the aircraft.
Another prior solution is described in U.S. Pat. No. 5,645,250 to D. Gevers. In this instance, the span of a wing attached to a fuselage is extended to lengthen an existing wing. This solution does not provide the desirable transition from high-aspect-ratio, low-speed aerodynamic characteristics to low-aspect-ratio, high-speed aerodynamic characteristics necessary to perform a multi objective missions.